Vacuum arc x-ray tube



July 5, 1966 w. P. DYKE ETAL 3,259,773

VACUUM ARC X-RAY TUBE Filed Sept. 25, 1961 Fig. 6

IN VEN TORS.

WALTER f? DYKE y FRANK J. GRUNDHAUSER BUCKHORN, CHEATHAM 8 BLOREATTORNEYS used the tubes had a short useful life.

United States Patent 3,259,773 VACUUM ARC X-RAY TUBE Walter P. Dyke andFrank J. Gruudhauser, McMinnville, 0reg., assignors to Field EmissionCorporation, McMinnville, Oreg., a corporation of Oregon Filed Sept. 25,1961, Ser. No. 141,260 12 Claims. (Cl. 313-57) This invention relates toa vacuum arc X-ray tube and more particularly to an X-ray tube having ananode of thin sheet metal positioned so that it is struck by rapidlymoving electrons emitted from a cathode as the result of a highintensity vacuum arc electric discharge between the cathode and anode,such electrons being focused upon a restricted area of one surface ofthe anode so that they puncture the anode and produce a pulse of highintensity X-ray radiation from the side of such anode remote from thecathode.

The X-ray tubes of the present invention employ a cathode having atleast one sharp needle point spaced from and directed toward a surfaceof a thin sheet metal anode. In operation a high current, high voltage,pulse of electrical energy is impressed across the gap between the anodeand cathode to produce a high intensity vacuum arc electrical dischargeof short duration. During such discharge, electrons emitted from thecathode point or points strike the anode at very high velocity. They arefocused upon a restricted area of the anode by either electrostatic orelectromagnetic focusing and penetrate and puncture the anode. As aresult an intense pulse of X-ray radiation is produced from the side ofthe anode opposite the cathode. Since such radiation is from arestricted area, for example one having a diameter of the order of 1mm., high resolution is obtained producing very sharp radiographs. Theanode is sufficiently thick that substantially all of the electrons havea single collision withan atom in the metal but such anode is alsosufiiciently thin that few, if any, electrons have multiple collisionsso that a narrow range of X-ray spectron is produced. Under theseconditions the focusing of the rapidly traveling electrons upon arestricted area causes a hole of approximately the size of suchrestricted area to be produced in the anode so that such area of theanode is destroyed. Certain of the tubes in accordance with the presentinvention are rendered inoperative as a result of one operation of thetube although in other tubes the area of the anode upon which theelectrons are focused may be shifted for successive operations so thatsuch tubes are capable of a plurality of operations.

Vacuum arc X-ray tubes employing a supplemental or starting anode inaddition to a main anode have been suggested. Initial ionization isproduced in such tubes by a spark or are in a short gap between thestarting anode and the cathode. Current flow across such gap is limitedby a high resistance in series with the starting anode. The initialionization enables an arc to be established across a much longer gapbetween the main anode and the cathode. In such tubes the anodes werethick structures and the useful X-ray radiation was from the surfacedirected toward the cathode. The area struck by the electrons has beenof the order of 1 cm. in diameter. Such tubes did not produce the highintensity nor the high resolution of the present tubes and were erraticin operation so that accurately timed pulses were not obtained. Eventhough relatively massive electrodes were Furthermore, the manner ofinitiating the discharge and the large size electrodes made theproduction of extremely narrow pulses with high rise time impossible.For example, the rise time of the current pulses were of the order ofseveral microseconds, whereas the present tubes can be ice constructedwith small electrodes having low inductance and capacitance so thataccurately formed X-ray pulses having a pulse width extending into thenanosecond range (10 seconds) including the rise time can be produced.Also the initiation of the discharge by employing a needle point cathodeenables precise timing of such discharge. The sharp needle cathodesincrease the electric field for a given voltage so as to cause the arcto be initiated early in the voltage pulse and independently ofelectrode imperfections or irregularities.

An X-ray tube employing a vacuum are initiated by a discharge from oneor more needle points in conjunction with an anode of sufiicientthickness that the anode is not punctured is described and claimed inthe copending application of the present applicants, Serial No. 114,125,filed June 1, 1961, now Patent No. 3,174,043. The most intense X-rayradiation is from the surface of the anode directed toward the cathodeand which is struck by the rapidly moving electrons. With such tubes theusable X-rays are those emitted at a substantial angle to the normal tothe anode surface, which X-rays are less intense than those emitted in adirection substantially normal to such surfaces. Such tubes can beconstructed to have long useful lives, for example, many thousands ofoperations. They produce relatively high intensity and resolution incomparison with the tubes described above employing a starting anode andare capable of producing accurately-timed X-ray pulses having pulselengths of the order of 10" seconds. In the tubes of the presentinvention, the most useful X-rays are those emitted from the surface ofthe anode opposite the cathode in a direction substantially normal tosuch surface, i.e. in the original direction of travel of the electrons.With the tubes of the present invention, it is possible to produceX-rays having several times the intensity of those produced with thesame amount of electrical power by tubes employing an anode which isthick enough to resist puncturing by a high intensity vacuum arc.

The tubes of the present invention require no heater power and may beconnected to the power source or pulser through a single transmissionline such as a coaxial cable or a cable having two inner conductors ofany reasonable length so as to be remotely located. Also the impedancesof the power source, cable and tube can be matched to provide formaximum transfer of power with minimum distortion of the pulse shape.Also the tubes can be made small in size so as to be capable of beinginserted into openings in objects to be X-rayed such as an opening in ahollow explosive or of being introduced into organs of the body such asthe stomach. Such tubes require a minimum of labor and materials andprovide improved reliability.

The anode of a tube of the present invention may form a part of theevacuated envelope of the X-ray tube. For example, such anode may be awindow of thin sheet metal in an otherwise normally thick'walledenvelope. The resulting X-ray tube is a destructible or expendable tube,since one operation of the tube renders it inoperative, at least until anew window is applied to the tube and the tube re-evacuated. Such tubesare particularly applicable to being employed in environments in whichthe tubes are destroyed in any event, for example, in an environmentwhere X-ray photographs of the behavior of a structure during anexplosion are being made and the X-ray tubes are destroyed by theexplosion. Such tubes produce the highest possible intensity of X-rayradiation, since the X-rays do not have to pass through any layer ofsolid material before reaching the object to be X-rayed.

Very high intensity X-rays may, however, also be generated in tubesemploying a thin sheet metal anode located Patented July 5, 1966 uentirely within an evacuated envelope and spaced from a cathode of thetype briefly described above. Simple tubes capable of a single operationonly and particularly usable in environments where the tube is destroyedcan also be provided although it is entirely possible to providemultiple operation tubes by causing the high intensity beam of electronsto strike different areas of the anode in subsequent operations. Itmagnetic focusing of the electrons upon the anode is employed, thedirection of the focusing magnetic field can be varied to focus theelectrons on different areas of the anode in successive operations ofthe tube, or alternatively with either type of focusing the anode can bemade movable relative to the cathode and provision made for moving theanode from the exterior of the tube to position different areas of theanode in the path of the rapidly traveling electrons. A considerablenumber of repeat operations can thus be carried out with a single tube.

It is therefore an object of the present invention to provide an vacuumarc X-ray tube in which a puncturable anode is employed to enable highintensity X-rays to be produced.

Another object of the invention is to provide an X-ray tube in which ahigh intensity vacuum arc can be produced to cause electrons to travelat high speed from a cathode to an anode of thin sheet metal to therebypuncture such anode and produce a high intensity pulse of X-rayradiation from the surface of the anode which is remote from thecathode.

A further object of the invention is to provide a vacuum arc X-ray tubein which a high intensity pulse of electrical energy is produced betweenone or more needle points carried by a cathode and a thin sheet metalanode so as to cause electrons to travel at high velocity from thecathode to the anode and in which tube such electrons are focused on arestricted area of the anode so as to puncture the anode and therebyproduce high intensity X-ray radiation from the surface of the anoderemote from the cathode.

A still further object of the invention is to provide a high intensityvacuum arc X-ray tube for pulse operation in which electrons travelingfrom a cathode to an anode in a vacuum arc of short duration are focusedupon laterally spaced areas of a thin sheet metal anode in successiveoperations of the tube so that such anode may be punctured during eachof such operations but the tube may be employed for repeated operations.

Other objects and advantages of the invention will appear in thefollowing detailed description of various embodiments thereof shown inthe attached drawings of which:

FIG. 1 is a longitudinal sectional view of an X-ray tube in accordancewith the present invention adapted for magnetic focusing and shown asbeing mounted in a metallic casing having a magnetic focusing element;

FIG. 2 is a longitudinal sectional view through a modified tube inaccordance with the present invention employing electrostatic focusing;

FIG. 3 is a fragmentary view of a further modified tube employingelectrostatic focusing and a movable anode;

FIG. 4 is a view similar to FIG. 2 of a modified tube employingelectromagnetic focusing and shown in conjunction with a magneticfocusing element;

FIG. 5 is a fragmentary isometric view of the anode of the tube of FIG.5; and

FIG. 6 is a view similar to FIG. 2, showing a further modified tubehaving separate reentrant portions extending from the same end of thetube for supporting the cathode and anode.

Referring more particularly to the drawings, the tube of FIG. 1 has anevacuated glass envelope 10 of elongated tubular form. The envelope 10has a tubular reentrant portion 12 in the inner end of which is sealed apair of spaced cathode supports 14 which are adapted to make contactwith a pin 16 attached to the inner conductor of a coaxial cable 18.Such cable has an insulating body 20 from which the outer conductor 22has been stripped for a portion of its length to enable the insulatingbody 29 to be inserted within the reentrant portion 12.

A cathode member 24 having a plurality of closely spaced needle points26 is supported on the ends of the cathode supports 14 so that theneedle points 26 are directed axially of the tube toward the surface ofan anode 28. The anode 23 is a small circular piece of thin sheet metalbrazed, welded or otherwise secured to an annular metal member 30forming a closure member for the end of the tube opposite the reentrantportion 12. The anode 28 is positioned to close an aperture 32 in suchmetal member. The metal member 30 may be made of any one of severalknown alloys which have a thermal coefficient of expansion substantiallythe same as that of the glass of the envelope 10 in contact with suchmember. Such annular member 30 is sealed directly to the anode end ofthe glass envelope 10.

The envelope 10 of the X-ray tube is shown as being mounted in a socket34 in a cylindrical member 36 of insulating material in turn positionedwithin a metal casing 38. The external portion of the cylindrical member36 adjacent the anode end of the tube is cut away to provide room for amagnetic focusing structure including a coil support 40 containing acoil 42 imbedded in insulating material. The coil 42 can be energized bydirect current to provide an adjustable focusing electromagnetic fieldextending axially of the tube. The coil support 40 has a nonmagneticmetal casing member 43 screwthreaded into the anode end of tubularcasing 38. The casing member 43 has an internal flange 44 which bearsagainst the annular closure member 30 of the tube in order to hold thetube and the insulating member 36 in the casing 38. The outer conductor22 of the coaxial cable may be connected to the casing 38 so that suchcasing and the casing member 43 form a continuation of such outerconductor. It will be apparent that the tube and its mounting shown inFIG. 1 provides a continuation of the coaxial structure of the coaxialcable 18 which will have a characteristic impedance of the same order asthat of the coaxial cable.

A high current, high voltage pulse of electrical energy may be deliveredto the tube shown in FIG. 1 from an electric pulse generating device ofthe general type shown in the copending application of Dyke et al.,Serial No. 103,796, filed April 18, 1961. Such pulses of electricalenergy may, for example, have voltages ranging from kilovolts to 2megavolts or higher and currents ranging from 1000 to 100,000 amperes orhigher, with the length of the pulse varying, for example, from .001 to.5 microsecond. The cathode needle points may have tip curvatures with aradius ranging from 10* to 10* centimeters and if a plurality areemployed, may be spaced from 1 to 30 mils apart and may project fromtheir supports, for example, a distance of the order of 50 mils. Methodsof making and mounting such needle points are discussed in the copendingapplication of Dyke et al., Serial No. 114,125 filed June 1, 1961, nowPatent No. 3,174,043. If a single needle point is employed it will, ingeneral, have its end melted and vaporized by the arc and if a pluralityof such points are employed on the cathode, usually two or three of suchpoints will have their ends vaporized, in which event, any subsequentdischarge in another operation of the tube will, in general, occur fromother points. The anode is, in general, made as thin as practicable formechanical. strength reasons and may, for example, be as thin as .0005inch for the lower voltages mentioned above, while for the highervoltages somewhat thicker anodes up to approximately .01 inch aresuitable. The preferred metal for both the anode and the cathode pointsis tungsten although. other metals may be employed, as the nature of theelectrode metals is not as critical as is the case with tubes intendedfor a large number of successive operations. As stated above, therapidly traveling electrons can be focused upon a spot on the surface ofthe anode of relatively small area by means of a magnetic field producedby the coil 42 so that the anode is punctured by such electrons. At thehigher voltages the intensity of the X-rays may be, for example, two orthree times that obtained with solid nondestructible anodes.

Instead of employing magnetic focusing of the electrons in the vacuumarc, electrostatic focusing can be employed, for example, in a tubestructure such as shown in FIG. 2. The tube of FIG. 2 includes anevacuated glass envelope 46 having a reentrant tubular portion 48 in theinner end of which is sealed a cathode support 50. Such support has ametallic focusing cup 52 secured to its exposed end so that the cup isdirected axially toward an anode 53 supported at the other end of thetube. A cathode member 54 having a plurality of needle points 26 alsodirected toward the anode 53 is mounted within the cup 52 so that theelectric field between the cathode cup 52 and the anode 53 during thevacuum arc discharge focuses the electrons traveling from the cathodetoward the anode onto a relatively small area on a surface of the anode.The anode 53 is a thin sheet metal member secured to and closing anaperture in a conical portion 58 of an annular closure member 60 for theend of the tube.- The closure member 68 maybe of a suitable metal sealedto the end of the envelope 46 in the same manner that the annular member30 of the tube of FIG. I is sealed to the end of the envelope 10. Thecathode support 50 may have a socket member 62 secured to its other endand positioned within the reentrant portion 48. It will be apparent thatthe tube of FIG. 2 can be mounted in a casing of the general type shownin FIG. 1 and connected to a coaxial cable so as to provide acontinuation of the coaxial structure of such cable. The focusing cup 52takes the place of the focusing coil 42 of FIG. 1 but otherwise theoperation of the tube may be similar to that of the tube of FIG. 1.

A modified tube employing electrostatic focusing and having an anodepositioned entirely within the envelope 64 of the tube and providing fora limited number of repeated operations of the tube is shown in FIG. 3.Such tube has a cathode cup 52 which may be supported on a support 50.The cup 52' of FIG. 3 may be of the same form as the cup 52 shown inFIG. 2 and may have a cathode member 54 supported therein and providedwith needle points 26 directed toward an anode 66. Such anode may be afrusto-conical member of thin sheet metal supported for rotation aboutits conical axis on an anode support 68 extending laterally through andsealed in a wall of the envelope 64. The large end of the frustoconicalanode member 66 may have a supporting rim '70 of metal wire securedthereto upon which are mounted a plurality of small magnetic elements72. The anode is positioned so as to have a part of its conical wallaligned with the cathode cup 52 and points 26. It will be apparent thatthe anode 66 may be rotated by employing a magnet located exteriorly ofthe envelope 64 so as to selectively position different portions of theanode 66 in position to receive electrons from the cathode 52 as theresult of establishing a vacuum are between the cathode and anode asdescribed above. The X-r-ays emitted from the anode 66 of FIG. 3 musttravel through the glass envelope 64 of the tube and are to some extentthereby diminished, but the intensity of such X-rays are substantiallygreater than from previously employed thick anodes.

Another modification of a tube in accordance with the invention is shownin FIG. 4 in which a cathode support 74 is sealed in the inner end of atubular reentrant portion 76 of a tube envelope 78. A cathode 80 in theform of a Wire carrying a plurality of closely spaced needle points 82directed toward a surface of an anode 84 of thin sheet metal is carriedby the end of the cathode 6 support 74. The end of the cathode support74 Within the reentrant portion 76 may be provided with a socket 62which may be similar to the socket 62 of FIG. 2 for receiving a pinconnected to the inner conductor of a coaxial cable.

The anode 84 of the tube of FIG. 4 may be a single piece of thin sheetmetal, such asfoil, folded into the shape shown in FIGS. 4 and 5 andsecured to an anode support 86 in any suitable manner such as by, spotwelding. The support 86 extends through and is sealed in the end of theenvelope 78 opposite the reentrant portion 76. A magnetic focusingstructure 88 surrounds the anode end of the tube and has a magnetic coil89 positioned therein. Direct current flowing through such magnetic coilprovides a field extending between the cathode and anode, which can beadjusted to the correct intensity to focus electrons from the cathodepoints 82 upon a small area on the portion 90 of the anode toward whichthe points 82 are directed. It will be apparent that the focusingstructure 88-may be tipped with respect to the envelope for the tube 78or alternatively the envelope of the tube may be adjusted throughvarious angles with respect to the focusing structure so that theorientation of the magnetic field with respect to the cathode and theanode can be varied to laterally shift the area upon which the electronsfrom the cathode are focused during successive operations of the tube.The tube of FIG. 4 can thus be employed for -a limited number ofrepeated operations.

The tube shown in FIG. 6 includes a tube envelope 91 in which twoseparate reentrant portions 92 and 94 extend from the base of the tubein parallel spaced relationship. One of such reentrant portions 92 has acathode support 96 sealed in its end. The support 96 has a reverse bend98 and supports a cathode 84 which maybe of the same type as the cathode84 of FIGS. 4 and 5. An anode support 74 and anode of the same form asthe support 74 and anode 80 of FIG. 4 is supported in the reentrantportion 94 and both of the supports 78 and 96 have socket members 62secured to their ends within the respective reentrant members. Thecathode is provided with a plurality of needle points 82 which aredirected toward the portion of the anode 84. The tube of FIG. 6 isparticularly adapted for connection to the end of a transmission line.cable having two inner'conductors insulated from each other and from anexternal shield. The two inner conductors of such cable can each beconnected to one of the sockets 62 of FIG. 6 and a casing ofthe generaltype shown in FIG. 1 can form a continuation of the external shield ofthe cable. It will be apparent that the tube of FIG. 6 is adapted formagnetic focusing of the electrons from the cathode 80 on the anode 84.

It will be further apparent that the tubes of the present invention areintended for a single or a limited number of operations and that eachoperation produces an intense pulse of X-rays from a small area and fora very short period of time. Such operation of- X-ray tubes is ofimportance where it is desired to take X-ray photographs throughextremely thick sections without long exposu-res and particularly whereit is desirable to stop. rapid motion of elements or parts positionedwithin other objects having relatively thick wall portions. The tubeswhich are intended for single operation have particular utility wherethe tube itself is destroyed, for example, by an explosion, the resultsof which it is desired to record by an X-ray photograph.

It will be apparent from the above description of the variousembodiments of the invention that the details of such embodiments may bevaried and that the invention is not limited .to such detailsbut thatits scope is to be determined by the following claims.

We claim:

1. A vacuum arc X-ray tube, which comprises:

an evacuated envelope,

an anode of thin sheet metal positioned to. have at least one surfaceexposed in the interior ofsaidtenvelope,

a cathode having at least one cathode element positioned in saidenvelope, said cathode element having a sharp field emission portionwith a radius of curvature less than 10- centimeters and being spacedfrom and directed toward said surface of said anode,

and electrical connection means leading to said cathode and anode sothat a high voltage, high current, pulse electric discharge can beproduced between said cathode and said anode to puncture said anode andsimultaneously produce a pulse of high intensity X-ray radiation fromthe surface of said anode remote from said cathode.

2. A vacuum arc X-ray tube, which comprises:

an evacuated envelope,

an anode of thin sheet metal forming a part of the wall of said envelopeand having one surface exposed in the interior of said envelope,

a cathode having at least one cathode element positioned in saidenvelope, said cathode element having a sharp field emission portionwith a radius of curvature less than 10- centimeters and being spacedfrom and directed toward said surface of said anode,

and electrical connection means leading to said cathode and anode sothat a high voltage, high current, pulse electric discharge producedbetween said cathode and said anode will puncture said anode andsimultaneously produce a pulse of high intensity X-ray radiation fromthe surface of said anode remote from said cathode.

3. A vacuum arc X-ray tube, which comprises:

an evacuated envelope,

an anode of thin sheet metal supported within said envelope,

a cathode having at least one cathode element positioned in saidenvelope, said cathode element having a sharp field emission portionwith a radius of curvature less than 10' centimeters and being spacedfrom and directed toward a surface of said anode,

and means for connecting said cathode and anode to a source of highvoltage, high current pulses capable of producing a vacuum are betweensaid cathode and anode so that a high voltage, high current,'pulseelectric discharge produced between said cathode and said anode willpuncture said anode and simultaneously produce a pulse of high intensityX-ray radiation from the surface of said anode remote from said cathode.

4. A vacuum arc X-ray tube, which comprises:

an evacuated envelope,

an anode of thin sheet metal supported by said envelope and having anelectron receiving surface on one side thereof exposed in said envelope,

a cathode supported by said envelope and having a plurality of spacedneedle points in said envelope and directed toward and spaced from saidsurface,

electrical connections leading to said cathode and anode so that a highvoltage, high current, pulse electric discharge can be produced betweensaid cathode and said anode,

and means for focusing electrons traveling at high velocity from saidcathode as a result of said discharge upon a restricted area of saidsurface so as to cause said electrons to puncture said restricted areaof said anode and simultaneously produce an intense pule of X-rayradiation from the surface of said anode remote from said cathode.

5. A vacuum arc X-ray tube, which comprises:

an evacuated envelope,

an anode of thin sheet metal supported by and forming a part of the wallof said envelope and having an electron receiving surface on one sidethereof exposed in said envelope,

a cathode supported by said envelope and having a plurality of spacedneedle points in said envelope and directed toward and spaced from saidsurface,

electrical connections leading to said cathode and anode so that a highvoltage, high current, pulse electric discharge can be produced betweensaid cathode and said anode,

and means for focusing electrons traveling at high velocity from saidcathode as a result of said discharge upon a restricted area of saidsurface so as to cause said electrons to puncture said restricted areaof said anode and simultaneously produce an intense pulse of X-rayradiation from the surface of said anode remote from said cathode.

6. A vacuum arc X-ray tube, which comprises:

an evacuated envelope,

an anode of thin sheet metal supported within said envelope and havingan electron receiving surface on one side thereof exposed in saidenvelope,

a cathode supported by said envelope and having a plurality of spacedneedle points in said envelope and directed toward and spaced from saidsurface,

electrical connections leading to said cathode and anode so that a highvoltage, high current, pulse electric discharge can be produced betweensaid cathode and said anode,

and means for focusing electrons traveling at high velocity from saidcathode as a result of said discharge upon a restricted area of saidsurface so as to cause said electrons to puncture said restricted areaof said anode and simultaneously produce an intense pulse of X-rayradiation from the surface of said anode remote from said cathode.

7. A vacuum arc X-ray tube having a puncturable anode, which tubecomprises:

an evacuated envelope,

an anode of thin sheet metal supported by said envelope and having anelectron receiving surface on one side thereof exposed in said envelope,

a cathode supported in said envelope and having a plurality of spacedneedle points directed toward and spaced from said surface,

electrical connections leading to said cathode and anode so that a highvoltage, high current, pulse electric discharge can be produced between.said cathode and said anode,

and electrostatic focusing means for focusing electrons traveling athigh velocity from said cathode as a result of said discharge upon arestricted area of said surface so as to cause said electrons topuncture said anode and simultaneously produce an intense pulse of X-rayradiation from the surface of said anode remote from said cathode.

8. A vacuum arc X-ray tube having a puncturable anode, which tubecomprises:

an evacuated envelope,

an anode of thin sheet metal supported by said envelope and having anelectron receiving surface on one side thereof exposed in said envelope,

a cathode supported in said envelope and having a plurality of spacedneedle points directed toward and spaced from said surface,

electrical connections leading to said cathode and anode so that a highvoltage, high current, pulse electric discharge can be produced betweensaid cathode and said anode,

and electromagnetic focusing means for focusing electrons traveling athigh velocity from said cathode as a result of said discharge upon arestricted area of said surface so as to cause said electrons topuncture said anode and simultaneously'produce an intense pulse of X-rayradiation from the surface of said anode remote from said cathode.

9. A vacuum arc X-ray tube having a destructible anode, which comprises:

an envelope having a vacuum therein,

an anode of thin sheet metal supported by said envelope and having anelectron receiving surface exposed in said envelope,

a cathode supported by said envelope and having at least one needlepoint in said envelope spaced from and directed toward said surface,

means to focus electrons traveling at high velocity from said point upona restricted area of said surface when a high cur-rent, high voltage,electric pulse discharge is produced between said cathode and said anodeso that said electrons puncture said anode and a pulse of high intensityX-ray radiation is produced from the surface of said anode opposite saidcathode,

and means to vary the position of said area on said anode during asubsequent electric pulse discharge to enable a repeated operation ofsaid tube.

10. A vacuum arc X-ray tube having a destructible anode, whichcomprises:

an envelope having a vacuum therein,

an anode of thin sheet metal supported by said envelope and having anelectron receiving surface exposed in said envelope,

a cathode supported by said envelope and having at least one needlepoint in said envelope spaced from and directed toward said surface,

means to focus electrons traveling at high velocity from said point upona restricted area of said surface when a high current, high voltage,electric pulse discharge is produced betweensaid cathode and said anodeso that said electrons puncture said anode and a pulse of high intensityX-ray radiation is produced from the surface of said anode opposite saidcathode,

and means to vary the position of said area on said anode during asubsequent electric pulse discharge to enable a repeated operation ofsaid tube,

including a support for said anode providing for changing the positionof said anode in said envelope relative to said cathode.

11. A vacuum arc X-ray tube having a destructible anode, whichcomprises:

an envelope having a vacuum therein,

an anode of thin sheet metal supported by said envelope and having anelectron receiving surface exposed in said envelope,

a cathode supported by said envelope and having a plurality of closelyspaced needle points in said envelope spaced from and directed towardsaid surface,

means to focus electrons traveling at high velocity from said point upona restricted area of said surface when a high current, high voltage,electric pulse discharge is produced between said cathode and said anodeso that said electrons puncture said anode and a pulse of high intensityX-ray radiation is produced from the surface of said anode opposite fromsaid cathode,

and means to vary the position of said area on said anode during asubsequent electric pulse discharge to enable repeated operation of saidtube.

12. A vacuum are X-ray tube having a destructible anode, whichcomprises:

an envelope having a vacuum therein,

an anode of thin sheet metal supported by said envelope and having anelectron receiving surface exposed in said envelope,

a cathode supported by said envelope and having at least one needlepoint in said envelope spaced from and directed toward said surface,

magnetic focusing means for producing a magnetic field to focuselectrons from said point upon a restricted area of said surface when ahigh current, high voltage electric pulse discharge is produced betweensaid cathode and said anode so that said electrons puncture said anodeand a pulse of high intensity X-ray radiation is produced from thesurface of said anode opposite said cathode,

and means to vary the direction of said field relative to said anode tovary the position of said area on said anode during a subsequentelectric pulse discharge to enable repeated operation of said tube.

References Cited by the Examiner UNITED STATES PATENTS 2,090,636 8/ 1937Olshevsky 313-59 2,277,712 3/1942 Otto 3l3351 2,329,318 9/ 1943 Atlee eta1. 313-57 2,392,380 1/1946 Varian 313-56 2,817,002 12/1957 Dyke et al313309 2,919,362 12/ 1959 Atlee 313- GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner.

W. F. LINDQUIST, P. C. DEMEO, Assistant Examiners.

1. A VACUUM ARC X-RAY TUBE, WHICH COMPRISES: AN EVACUATED ENVELOPE, ANANODE OF THIN SHEET METAL POSITIONED TO HAVE AT LEAST ONE SURFACEEXPOSED IN THE INTERIOR OF SAID ENVELOPE, A CATHODE HAVING AT LEAST ONECATHODE ELEMENT POSITIONED IN SAID ENVELOPE, SAID CATHODE ELEMENT HAVINGA SHARP FIELD EMISSION PORTION WITH A RADIUS OF CURVATURE LESS THAN 10-3CENTIMETERS AND BEING SPACED FROM AND DIRECTED TOWARD SAID SURFACE OFSAID ANODE, AND ELECTRICAL CONNECTION MEANS LEADING TO SAID CATHODE ANDANODE SO THAT A HIGH VOLTAGE, HIGH CURRENT, PULSE ELECTRIC DISCHARGE CANBE PRODUCED BETWEEN SAID CATHODE AND SAID ANODE TO PUNCTURE SAID ANODEAND SIMULTANEOUSLY PRODUCE A PULSE OF HIGH INTENSITY X-RAY RADIATIONFROM THE SURFACE OF SAID ANODE REMOTE FROM SAID CATHODE.